Pretty much what the title says.
Got a question? Throw it at me and I'll try my best to answer.

My knowledge is not just limited to this so I'll try my best, if I can't, anybody else who might know, can take up and answer

Let's do the community a good deed.

Forum, Host, and Domain Helpdesk? Can you elaborate a bit more, please?

Related to forum software, I expertise in myBB, PhpBB, punBB, vBulletin, IPB, Xenforo.
Related to hosts, I used to manage a hosting company for my bud back in 2008, for around 5 years. I can do a lot of stuff that you're confused with due to hosts.
Related to domains, many people are stuck in doing DNS, or learning how to forward a domain, or make an email for one.
I'll provide support for this.

I'm certain people who don't understand can quite simply open a thread or contact their host's technical support.

how can i put my domain on my fourum?

It is really simple, all you need to do is forward your domain's NS(nameservers) 1 and 2 to the host where your forum is hosted's name servers. To do this, contact the host's support and ask them what their NS are. Once you get to know them, in Domain you should have an option to change your DNS, there you can just add the IP.

Above scenario is in case you want your domain to redirect to your forum.

i downloaded smf to my computer, what now?

build wall around computer to protect against spam bots

Get a domain and redirect it to your IP instead of a host, since you want to home-host it.
If someone hits your website, you're going down too so rip.

redirect it to your IP? hmm, how do i do that good sir?